Depositing thin layers on a flexible substrate is a production process for many applications. The flexible substrates are thereby coated in one or more chambers of a flexible substrate coating apparatus. The flexible substrates, such as foils made of plastics or pre-coated papers, are guided on rolls or drums and pass in this way the source of deposition material. Possible applications of the coated substrate range from providing coated foils for the packaging industry to depositing thin films for flexible electronics and advanced technology applications, such as smartphones, flat screen TVs and solar panels.
Different deposition processes may be used to achieve a layer with the desired properties. For instance, in a thermal evaporation process, thin layers of aluminum are metallized onto flexible substrates. Substrates coated in such a way may for instance be used for the production of protective packaging or decorative materials. In further processes, such as in reactive coating processes, gas is supplied to the substrate additionally to an evaporated material from the material source in order to provoke a chemical reaction influencing the layer deposited on the substrate. By using such processes, several characteristics of the substrate may be controlled, such as barrier characteristics for water vapor or oxygen, and transparency characteristics of the finished product.
For the finished product, it is desirable to have a reliable and optically acceptable layer on the substrate in order to have a product of high quality. At the same time, the productivity of the deposition process has to be considered in so far as a slow process yielding a high quality product may not be acceptable for a customer due to the costs increasing with the production time. In known systems, the number of material sources may be adapted in order to improve the productivity, the guiding drums for the substrates may be adapted (such as cooled, or positioned in a suitable way) in order to achieve desired layer properties, and a control unit may monitor and optimize the process to avoid irregularities in the process operation.
However, irrespective of the measures taken, irregularities may still appear in the optical appearance of the coated substrate, which is not acceptable in case of packaging industry or decorative foils. In view of the above, it is an object of the present invention to provide an evaporation apparatus that overcomes at least some of the problems in the art.